In a current audio data transmission via an audio interface, different mobile terminals have different audio transmission characteristics. In order to be compatible with the audio transmission characteristics of different mobile terminals, an apparatus (such as an electronic signature token) communicating with the mobile terminal needs to try with audio data in different modulation modes automatically so as to find a most suitable modulation mode matched with each of the different mobile terminals.
Currently, there are few audio communication means, and consequently no suitable mode can be compatible with the communication between different mobile terminals and different electronic signature tokens.
Moreover, since both sides in the communication may not necessarily be fixed and can have their own different audio transmission characteristics, when the demodulation mode and the modulation mode not matched with each other are adopted during the audio data transmission, a data interaction speed may be reduced and it is easy for a distortion to occur in the interactive data.